1. Field of the Invention
The present invention relates to a diaphragm for use with an electro-acoustic transducer and a method of producing the same and, more particularly, to a diaphragm for use with an electro-acoustic transducer and a method of producing the same by using synthetic resin materials.
2. Background of the Invention
A method of producing a diaphragm for use with an electro-acoustic transducer which becomes a premise of the present invention will be described below with reference to FIG. 1a to 1d and FIGS. 2a to 2c of the accompanying drawings. The above-mentioned diaphragm for use with an electro-acoustic transducer will be referred to hereinafter simply as "diaphragm".
Initially, a member 31 of substantially truncated cone configuration shown in FIG. 1a is produced. The substantially truncated cone-shaped member 31 is produced by some suitable methods, such as sheet-making of paper and pulp, pressing of polymer film under heating or injection-molding of olefin thermoplastic resin. The substantially truncated cone-shaped member 31 is cut out at its portion shown by a one-dot chain line in FIG. 1a to provide an outer diameter portion 32 and a bottom portion 33. As a result, the member 31 is manufactured as a cone-shaped diaphragm member 34 shown in FIG. 1b.
A member 37 of substantially saucer configuration shown in FIG. 1c is produced by heating and molding a material, such as cotton cloth, rubber, polyurethan foam, elastomer or the like. The substantially saucer-shaped member 37 is cut out at its positions of diameters .phi.A and .phi.B shown by one-dot chain lines in FIG. 1c to provide an outer peripheral portion and an inner peripheral portion.
As a consequence, the substantially saucer-shaped member 37 is manufactured as an annular-shaped edge member 38 shown in FIG. 1d. The edge member 38 includes an edge portion 38a of substantially U-shaped cross section. To join the diaphragm member 34 and the edge member 38 thus formed, the diaphragm member 34 is coated at its outer surface portion of the outer peripheral side with an adhesive 35 as shown in FIG. 2a. Then, the edge member 38 is positioned on a mold 41 by engaging the edge portion 38a of the edge member 38 with a protrusion 41a of the mold 41 of the molds 40 and 41. Under this condition, an opening portion 34a of the diaphragm member 34 is fitted into a columnar portion 41a by downwardly inserting the diaphragm member 34 into the mold 41. The diaphragm member 34 is positioned on the mold 41. Subsequently, the mold is closed by lowering the mold 40 of the molds 40, 41 in FIG. 2b, and the diaphragm 34 and the edge member 38 are pressed. In this case, the molds 40, 41 are heated at a predetermined temperature, the adhesive 35 is cured under pressure produced when the molds 40, 41 are pressed. Consequently, as shown in FIG. 2c, the diaphragm member 34 and the edge member 38 are joined together.
According to the method of producing a diaphragm shown in FIGS. 1a to 1d and FIGS. 2a to 2c, the diaphragm member 34 and the edge member 38 are produced separately, and the diaphragm member 34 and the edge member 38 are manufactured as the predetermined shapes, whereafter the diaphragm member 34 and the edge member 38 are bonded together by the adhesive 35.
When however the diaphragm member 34 is made of olefin thermoplastic resin and the edge member 38 is made of synthetic rubber or elastomer, a pre-treatment should be carried out in order to improve an adhesive property. In the pre-treatment, after the diaphragm member 34 and the edge member 38 are manufactured as the predetermined shapes, either or both of the diaphragm member 34 and the edge member 38 are coated with a primer, whereafter the adhesive 35 is coated on the diaphragm member 34 and the diaphragm member 34 and the edge member 38 are bonded together by means of the adhesive 35. Therefore, the number of manufacturing processes is increased, which unavoidably increases the manufacturing cost of the diaphragm.
When the diaphragm member 34 and the edge member 38 are bonded together, the diaphragm member 34 and the edge member 38 should be bonded under the condition that a center of the diaphragm member 34 and a center of the edge member 38 are coincident with each other. If the center of the diaphragm member 34 and the center of the edge member 38 are displaced from each other after the diaphragm member 34 and the edge member 38 are bonded together, then the diaphragm cannot be vibrated correctly. Particularly, in the speaker apparatus of dynamic type, when the diaphragm is displaced in position, a voice coil bobbin that is attached to the diaphragm member also is displaced in position. There is then the new problem that a magnetic circuit is disturbed by the voice coil bobbin.
From an acoustic characteristic standpoint of the diaphragm, since the adhesive is interposed at the portion in which the outer peripheral edge of the diaphragm member and the inner peripheral edge of the edge member are bonded, the acoustic characteristic of the diaphragm and the quality of the diaphragm are influenced by the cured state of the adhesive and the types of the adhesives or the joined state of the diaphragm member and the edge member. As a result, the characteristic of the diaphragm thus mass-produced tends to become irregular. Therefore, it becomes impossible to obtain a diaphragm of high reliability. Moreover, when the diaphragm thus produced is used, it becomes impossible to mass-produce speaker apparatus of uniform tone quality.